Multi-speed gearbox

ABSTRACT

Multi-stage transmission comprising four planetary gear sets, eight rotatable shafts and six shift elements. Sun of first set is connected to eighth shaft connected to sun of second set and is connectable, via third clutch, to drive shaft. Drive shaft is connectable, via first clutch, to fourth shaft connected to carrier of first set and is couplable, via second brake, to housing. Drive shaft is connectable, via second clutch, to seventh shaft connected to carrier of fourth set and ring of third set, Sixth shaft is connected to ring of first set, carrier of second set and ring of fourth planetary gear set. Third shaft is connected to sun of third set and sun of fourth set and is couplable, via first brake, to housing. Fifth shaft is connected to ring of second set and is couplable, via third brake, to housing. Output shaft is connected to carrier of third set.

This application is a National Stage completion of PCT/EP2013/055071filed Mar. 13, 2013, which claims priority from German patentapplication serial no. 10 2012 206 817.1 filed Apr. 25, 2012.

FIELD OF THE INVENTION

The present invention relates to a multi-stage transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from DE 199 12 480B4 by the applicant. It comprises three single-carrier planetary gearsets, as well as three brakes and two clutches for shifting six forwardgears and one reverse gear, an input shaft and an output shaft, whereinthe carrier for the first planetary gear set is permanently connected tothe ring gear of the second planetary gear set, and the carrier for thesecond planetary gear set is permanently connected to the ring gear ofthe third planetary gear set, and the input shaft is directly connectedto the sun gear of the second planetary gear set.

Furthermore, in the known transmission, the input shaft is connectable,by means of the first clutch, to the sun gear of the first planetarygear set, and, by means of the second clutch, to the carrier of thefirst planetary set, wherein the sun gear of the first planetary gearset is connectable, by means of the first brake, to a housing of thetransmission, and the carrier of the first planetary gear set isconnectable, by means of the second brake, to the housing of thetransmission, wherein the sun gear of the third planetary gear set isconnectable, by means of the third brake, to the housing of thetransmission. The input shaft of the transmission is permanentlyconnected to the carrier for the third planetary gear set and the ringgear of the first planetary gear set.

Furthermore, a nine-speed multi-stage transmission is known from DE 2936 969 A1; it comprises eight shift elements and four planetary gearsets, wherein one planetary gear set serves as a front-mountedtransmission and the main gearing includes a Simpson set and a furtherplanetary gear set serving as a reverse gearing.

Further multi-stage transmissions are known, for example, from theapplicant's DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1.

Automatically shiftable vehicle transmissions of a planetary design arealready generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a small number of shift elements, and minimize the need fordouble shifting, i.e., engaging and/or disengaging two shift elements,when sequential shifting is performed, thereby ensuring that only oneshift element is ever switched when shifting is performed in definedgroups of gears.

The applicant's document, DE 10 2008 000 428 A1 discloses a multi-stagetransmission of a planetary design that includes an input shaft and anoutput shaft, which are disposed in a housing. In the knowntransmissions, at least four planetary gear sets, referred to in thefollowing as the first, second, third and fourth planetary gear sets, atleast eight rotatable shafts, referred to in the following as the driveshaft, output shaft, third, fourth, fifth, sixth, seventh and eighthshafts, as well as at least six shift elements, comprising brakes andclutches, are provided, the selective engagement of which producesdifferent transmission ratios between the input drive and the outputdrive, so that preferably nine forward gears and one reverse gear can beimplemented,

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, thus having a negative stationarytransmission ratio, form a shiftable front-mounted gear set, wherein thethird and fourth planetary gear sets form a main gear set.

In the known multistage transmission, the carriers of the first andsecond planetary gear sets are coupled together, via the fourth shaft,which is connected to an element of the main gear set, the ring gear ofthe first planetary gear set is coupled to the sun gear of the secondplanetary gear set, via the eighth shaft, which is detachablyconnectable to the drive shaft via the first clutch, and the sun gear ofthe first planetary gear set can be coupled to a housing of thetransmission by means of the third shaft, via a first brake, and isdetachably connectable to the drive shaft, via a second clutch, whereinthe ring gear of the second planetary gear set can be coupled to ahousing of the transmission by means of the fifth shaft, via a secondbrake. In addition, the seventh shaft is permanently connected to atleast one element of the main gear set, and can be coupled to thehousing of the transmission, via a third brake, and the sixth shaft ispermanently connected to at least one further element of the main gearset and is detachably connectable to the drive shaft, via a thirdclutch; the output shaft is permanently connected at least to onefurther element of the main gear set.

In the known transmission, the fourth shaft is preferably permanentlyconnected to the ring gear of the third planetary gear set, the sixthshaft is permanently connected to the ring gear of the fourth planetarygear set and to the carrier of the third planetary gear set, and isdetachably connectable to the drive shaft, via the third clutch.Furthermore, the seventh shaft is permanently connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to ahousing of the transmission, via the third brake. In this case, theoutput drive is produced, via the output shaft, that is permanentlyconnected to the carrier of the fourth planetary gear set. Furthermore,the third and fourth planetary gear sets can be combined or reduced to aRavigneaux set having a common carrier and a common ring gear.

According to the prior art, the shift elements of multi-stagetransmission thus designed, which are usually designed as lamellarclutches or brakes, are actuated hydraulically, which disadvantageouslyresults in significant hydraulic losses. In order to avoid theseactuation losses, the use of shift elements that can be actuated upondemand would be especially advantageous.

In order to make it possible to use shift elements that can be actuatedupon demand, the shift elements, in particular the clutches, should beeasily accessible from outside.

Shift elements that can be actuated upon demand may be understood, inparticular, to be shift elements for maintaining the shift state, thuswhich use no energy or less energy, when disengaged or engaged, thanwhen altering the shift state.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a multi-stagetransmission of the initially described type, which has nine forwardgears and a reverse gear having a sufficient transmission ratio, inwhich the design complexity, the component load and the installationsize are optimized, and in which efficiency is improved. In addition,the shift elements of the transmission should be easily accessible fromoutside, which makes it possible to install shift elements that can beactuated upon demand. In addition, the transmission should be suitablefor standard design and for a frontal transverse design.

Accordingly, a multi-stage transmission, according to the invention, ofa planetary design is proposed which has an input shaft and an outputshaft, which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and six shift elements, preferably designed as lamellarshift elements or as a form locking shift element, comprising brakes andclutches, whose selective engagement produces different transmissionratios between the drive shaft and the output shaft, and, therefore,preferably nine forward gears and one reverse gear can be implemented.

The planetary gear sets of the transmission are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably carried, the planetary gears meshing with the sun gear and thering gear. As a result, when the carrier is fixed, the ring gear has adirection of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablycarried, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, and each inner planet gearmeshes with only one outer planet gear. As a result, when the carrier isfixed, the ring gear has the same direction of rotation as the sun gear,and a positive stationary transmission ratio results.

According to the invention, the sun gear of the first planetary gear setis connected to the eighth shaft, which is connected to the sun gear ofthe second planetary gear set and which can be detachably connected, viaa third clutch, to the drive shaft 1, wherein the drive shaft can bedetachably connected, via a first clutch, Ito the fourth shaft, which isconnected to the carrier of the first planetary gear set and which canbe coupled, via a second brake, to the housing. In addition, the driveshaft can be detachably connected, via a second clutch, to the seventhshaft, which is connected to the carrier of the fourth planetary gearset and the ring gear of the third planetary gear set.

In addition, the sixth shaft is connected to the ring gear of the firstplanetary gear set, the carrier of the second planetary gear set and tothe ring gear of the fourth planetary gear set, wherein the third shaftis connected to the sun gear of the third planetary gear set and the sungear of the fourth planetary gear set, and can be coupled, via a firstbrake, to the housing.

In addition, the fifth shaft is connected to the ring gear of the secondplanetary gear set and can be coupled, via a third brake, to thehousing, wherein the output shaft of the transmission is connected tothe carrier of the third planetary gear set.

Because the first, second and third clutch are disposed on the driveshaft of the transmission and the remaining shift elements are designedas brakes, good accessibility of all the shift elements of thetransmission is ensured, as a result of which the shift elements may bedesigned as shift elements that can be actuated upon demand. Within thecontext of further embodiments, shift elements of the transmission maybe designed, inter alia, as shift elements that can be hydraulicallyactuated.

In addition, transmission ratios are attained that are especiallysuitable for passenger vehicles, as well as a greater overall gear ratioof the multi-stage transmission, which results in improved drivingcomfort and a significant reduction in fuel consumption.

Furthermore, design complexity is significantly reduced with themulti-stage transmission, according to the invention, due to a lownumber of shift elements. Using the multi-stage transmission accordingto the invention, it is advantageously possible to perform a start-upusing a hydrodynamic converter, an external start-up clutch, or anyother suitable external start-up element. It is also conceivable toperform a start-up using a start-up element integrated in thetransmission. Preferably, a shift element that is actuated in the firstforward gear and in the reverse gear is suitable for this.

Moreover, the multi-stage transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Low torques are advantageously present in the shift elements and in theplanetary gear sets of the multi-stage transmission, therebyadvantageously reducing wear in the multi-stage transmission. Inaddition, the low torques make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following, as anexample, with reference to the attached Figures. They show:

FIG. 1: a schematic view of a preferred embodiment of a multi-stagetransmission according to the invention; and

FIG. 2: an example of a shift pattern for a multi-stage transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi-stage transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4 which are disposed in a housing G. In the exampleshown in FIG. 1, planetary gear sets P1, P2, P3 P4 are designed as minusplanetary gear sets. According to the invention, at least one of theplanetary gear sets P1, P2, P3, P4 can be implemented as a plusplanetary gear set if the carrier and ring gear connection are exchangedand, simultaneously, the value of the stationary transmission ratio isincreased by 1 in comparison to the embodiment as a minus planetary gearset.

In the embodiment shown here, viewed axially, the planetary gear setsP1, P2, P3, P4 are disposed in the sequence of the first planetary gearset P1, the second planetary gear set P2, the third planetary gear setP3, the fourth planetary gear set P4. According to the invention, theaxial sequence of the individual planetary gear sets and theconfiguration of the shift elements may be freely selected as long asthis allows the elements to connect.

As shown in FIG. 1, six shift elements are provided, namely, threebrakes, 03, 04, 05 and three clutches 14, 17, 18. The spatialdisposition of the shift elements can be arbitrary, and is limited onlyby the dimensions of the outer design. The clutches and the brakes ofthe transmission are preferably designed as friction elements orlamellar shift elements respectively; however they may also be designedas form-locking shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi-stage transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaftforms the first shaft, and the output shaft forms the second shaft ofthe transmission.

According to the invention, in the multi-stage transmission according toFIG. 1 it is provided that the sun gear of the first planetary gear setP1 is connected to the eighth shaft 8, which is connected to the sungear of the second planetary gear set P2 and which can be detachablyconnected, via a third clutch 18, to the drive shaft 1, wherein thedrive shaft 1 can be detachably connected, via a first clutch 14, to thefourth shaft 4, which is connected to the carrier of the first planetarygear set P1 and which can be coupled, via a second brake 04, to thehousing G. With reference to FIG. 1, the drive shaft 1 can be detachablyconnected, via a second clutch 17, to the seventh shaft 7, which isconnected to the carrier of the fourth planetary gear set P4 and thering gear of the third planetary gear set P3.

As is evident from FIG. 1, the sixth shaft 6 is connected to the ringgear of the first planetary gear set P1, the carrier of the secondplanetary gear set P2 and the ring gear of the fourth planetary gear setP4, wherein the third shaft 3 is connected to the sun gear of the thirdplanetary gear set P3 and the sun gear of the fourth planetary gear setP4, and can be coupled, via a first brake 03, to the housing G.

In addition, the fifth shaft 5 is connected to the ring gear of thesecond planetary gear set P2 and can be coupled, via a third brake 05,to the housing G, wherein the output shaft 2 of the transmission isconnected to the carrier of the third planetary gear set P3.

In connection herewith, viewed axially, the first, second and thirdclutches 14, 17, 18 may be disposed side by side and may be designed aslamellar shift elements and have a common external disk carrier. In theembodiment shown, in particular the first brake 03 is suited for designas a dog clutch element, which significantly improves fuel consumption.

FIG. 2 shows an example of a shift pattern of a multi-stage transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps and, to be determined therefrom, the gearincrements or step changes φ to the next higher gear, wherein the value9.011 is the transmission ratio spread.

In the example shown, the values for the stationary transmission ratiosof the planetary gear sets P1, P2, P3, P4, implemented as minusplanetary gear sets, are—−2.338, −1.600, −3.257 and −2.897 respectively.FIG. 2 shows that only one shift in element must be engaged and oneshift element must be disengaged when shifting sequentially, since twoneighboring gear steps jointly use two shift elements. It is also shownthat a large transmission ratio spread is attained with small gearincrements.

The first forward gear is attained by engaging the first and thirdbrakes 03, 05 and the third clutch 18, the second forward gear isattained by engaging the first and third brakes 03, 05 and the firstclutch 14, the third forward gear is attained by engaging the firstbrake 03 and the first and third clutches 14, 18, the fourth forwardgear is attained by engaging the first brake 03 and the second and thirdclutches 17, 18, the fifth forward gear, which is designed as a directgear in the example shown, is attained by engaging the first, second andthird clutches 14, 17, 18, the sixth forward gear is attained byengaging the third brake 05 and the first and second clutches 14, 17,the seventh forward gear is attained by engaging the third brake 05 andthe second and third clutches 17, 18, the eighth forward gear isattained by engaging the second and third brakes 04, 05 and the secondclutch 17 and the ninth forward gear is attained by engaging the secondbrake 04 and the second and third clutches 17, 18, wherein the reversegear is attained by engaging the first and second brakes 03, 04 and thethird clutch 18.

Alternatively, the fourth forward gear may be shifted by means ofadditional shift combinations, which are designated with an M in FIG. 2.Accordingly, the fourth forward gear can be attained by engaging thefirst and second brakes 03, 04 and the second clutches 17, or byengaging the first brake 03 and the first and second dutch 14, 17, or byengaging the first and third brakes 03, 05 and the second clutch 17.

Since the first, second and third brakes 03, 04, 05 and the third clutch18 are engaged in the first forward gear and/or in the reverse gear,these shift elements can be used as start-up elements.

According to the invention, different gear increments also result fromthe same shift pattern depending on the shift logic, thereby making itpossible to implement an application-specific or vehicle-specificvariation.

According to the invention, it is also optionally possible to provideadditional freewheels at each suitable location of the multi-stagedtransmission, for example, between a shaft and the housing, or possiblyto connect two shafts.

An axle differential and/or a distributor differential can be disposedon the drive side or on the output side.

Within the scope of an advantageous development of the invention, thedrive shaft 1 can be separated from a drive motor, as needed, by aclutch element, wherein a hydrodynamic converter, a hydraulic clutch, adry start-up clutch, a wet start-up clutch, a magnetic powder clutch, ora centrifugal clutch or the like can be used as the clutch element. Itis also possible to dispose such a start-up element in the power flowdirection after the transmission wherein, in this case, the drive shaft1 is permanently connected to the crankshaft of the drive motor.

The multi-stage transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the drive motorand the transmission.

Within the scope of a further, not depicted embodiment of the invention,a wear-free brake, for instance, a hydraulic or an electric retarder orthe like, can be disposed on each shaft, preferably on the drive shaft 1or the output shaft 2, which is, in particular, of special significancefor use in commercial vehicles. Furthermore, a power take-off drive canbe provided on each shaft, preferably on the input shaft 1 or the outputshaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi-stage transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

REFERENCE CHARACTERS

-   1 first shaft, drive shaft-   2 second shaft, output shaft-   3 third shaft-   4 fourth shaft-   5 fifth shaft-   6 sixth shaft-   7 seventh shaft-   8 eighth shaft-   03 first brake-   04 second brake-   05 third brake-   14 first clutch-   17 second clutch-   18 third clutch-   G housing-   P1 first planetary gear set-   P2 second planetary gear set-   P3 third planetary gear set-   P4 fourth planetary gear set-   i transmission ratio-   100 step change

1-7. (canceled)
 8. A multi-stage transmission of a planetary designcomprising: a drive shaft (1), an output shaft (2), first, second, thirdand fourth planetary gear sets (P1, P2, P3, P4) disposed within ahousing (G), third, fourth, fifth, six, seventh and eighth rotatableshafts (3, 4, 5, 6, 7, 8), and six shift elements (03, 04, 05, 14, 17,18), comprising brakes (03, 04, 05) and clutches (14, 17, 18), whoseselective engagement produces different transmission ratios between thedrive shaft (1) and the output shaft (2) so that nine forward gears anda reverse gear are implementable, wherein the eighth shaft (8) isconnected to both the sun gear of the first planetary gear set (P1) andthe sun gear of the second planetary gear set (P2), and the eighth shaft(8) can be detachably connected, via a third clutch (18), to the driveshaft (1), the drive shaft (1) is detachably connectable, via a firstclutch (14), to the fourth shaft (4), the fourth shaft (4) is connectedto the carrier of the first planetary gear set (P1) and the fourth shaft(4) is couplable, via a second brake (04), to the housing (G), the driveshaft (1) is detachably connectable, via a second clutch (17), to theseventh shaft (7), the seventh shaft (7) is connected to both thecarrier of the fourth planetary gear set (P4) and the ring gear of thethird planetary gear set (P3), the sixth shaft (6) is connected to eachof the ring gear of the first planetary gear set (P1), the carrier ofthe second planetary gear set (P2) and the ring gear of the fourthplanetary gear set (P4), the third shaft (3) is connected to both thesun gear of the third planetary gear set (P3) and the sun gear of thefourth planetary gear set (P4), and the third shaft (3) can be coupled,via a first brake (03), to the housing (G), the fifth shaft (5) isconnected to the ring gear of the second planetary gear set (P2) and iscouplable, via a third brake (05), to the housing (G), and the driveshaft (2) is connected to the carrier of the third planetary gear set(P3).
 9. The multi-stage transmission according to claim 8, wherein thefirst, second, third and fourth planetary gear set (P1, P2, P3, P4) aredesigned as minus planetary gear sets.
 10. The multi-stage transmissionaccording to claim 8, wherein, when viewed axially, the first, thesecond, the third and the fourth planetary gear sets are disposed in thesequence of the first planetary gear set (P1), the second planetary gearset (P2), the third planetary gear set (P3) and the fourth planetarygear set (P4).
 11. The multi-stage transmission according to claim 8,wherein the shift elements (03, 04, 05, 14, 17, 18) of the transmissionare designed as shift elements that can be actuated upon demand.
 12. Themulti-stage transmission according to claim 8, wherein the first brake(03) is designed as a form-locking shift element.
 13. The multi-stagetransmission according to claim 8, wherein a first forward gear isattained by engaging the first and the third brakes (03, 05) and thethird clutch (18), a second forward gear is attained by engaging thefirst and the third brakes (03, 05) and the first clutch (14), a thirdforward gear is attained by engaging the first brake (03) and the firstand the third clutches (14, 18), a fourth forward gear is attained byengaging the first brake (03) and the second and the third clutches (17,18), a fifth forward gear is attained by engaging the first, the secondand the third clutches (14, 17, 18), a sixth forward gear is attained byengaging the third brake (05) and the first and the second clutches (14,17), a seventh forward gear is attained by engaging the third brake (05)and the second and the third clutches (17, 18), an eighth forward gearis attained by engaging the second and the third brakes (04, 05) and thesecond clutch (17), a ninth forward gear is attained by engaging thesecond brake (04) and the first and the third clutches (17, 18), and thereverse gear is attained by engaging the first and the second brakes(03, 04) and the third clutch (18).
 14. The multi-stage transmissionaccording to claim 8, wherein a first forward gear is attained byengaging the first and the third brakes (03, 05) and the third clutch(18), a second forward gear is attained by engaging the first and thethird brakes (03, 05) and the first clutch (14), a third forward gear isattained by engaging the first brake (03) and the first and the thirdclutches (14, 18), a fourth forward gear is attained by engaging thefirst and the second brakes (03, 04) and the second clutch (17), a fifthforward gear is attained by engaging the first, the second and the thirdclutches (14, 17, 18), a sixth forward gear is attained by engaging thethird brake (05) and the first and the second clutches (14, 17), aseventh forward gear is attained by engaging the third brake (05) andthe second and the third clutches (17, 18), an eighth forward gear isattained by engaging the second and the third brakes (04, 05) and thesecond clutch (17), a ninth forward gear is attained by engaging thesecond brake (04) and the first and the third clutches (17, 18), and thereverse gear is attained by engaging the first and the second brakes(03, 04) and the third clutch (18).
 15. The multi-stage transmissionaccording to claim 8, wherein a first forward gear is attained byengaging the first and the third brakes (03, 05) and the third clutch(18), a second forward gear is attained by engaging the first and thethird brakes (03, 05) and the first clutch (14), a third forward gear isattained by engaging the first brake (03) and the first and the thirdclutches (14, 18), a fourth forward gear is attained by engaging thefirst brake (03) and the first and the second clutches (14, 17), a fifthforward gear is attained by engaging the first, the second and the thirdclutches (14, 17, 18), a sixth forward gear is attained by engaging thethird brake (05) and the first and the second clutches (14, 17), aseventh forward gear is attained by engaging the third brake (05) andthe second and the third clutches (17, 18), an eighth forward gear isattained by engaging the second and the third brakes (04, 05) and thesecond clutch (17), a ninth forward gear is attained by engaging thesecond brake (04) and the first and the third clutches (17, 18), and thereverse gear is attained by engaging the first and the second brakes(03, 04) and the third clutch (18).
 16. The multi-stage transmissionaccording to claim 8, wherein a first forward gear is attained byengaging the first and the third brakes (03, 05) and the third clutch(18), a second forward gear is attained by engaging the first and thethird brakes (03, 05) and the first clutch (14), a third forward gear isattained by engaging the first brake (03) and the first and the thirdclutches (14, 18), a fourth forward gear is attained by engaging thefirst and the third brakes (03, 05) and the second clutch (17), a fifthforward gear is attained by engaging the first, the second and the thirdclutches (14, 17, 18), a sixth forward gear is attained by engaging thethird brake (05) and the first and the second clutches (14, 17), aseventh forward gear is attained by engaging the third brake (05) andthe second and the third clutches (17, 18), an eighth forward gear isattained by engaging the second and the third brakes (04, 05) and thesecond clutch (17), a ninth forward gear is attained by engaging thesecond brake (04) and the first and the third clutches (17, 18), and thereverse gear is attained by engaging the first and the second brakes(03, 04) and the third clutch (18).
 17. The multi-stage transmissionaccording to claim 8, wherein the multi-stage transmission is anautomatic transmission for a motor vehicle.
 18. A multi-stagetransmission of a planetary design comprising: a drive shaft, an outputshaft, first, second, third and fourth planetary gear sets disposedwithin a housing, and each of the first, the second, the third and thefourth planetary gear sets comprising a sun gear, planet gears and aring gear, third, fourth, fifth, six, seventh and eighth rotatableshafts, and six shift elements, comprising brakes and clutches, whoseselective engagement produces different transmission ratios between thedrive shaft and the output shaft so that nine forward gears and areverse gear are implementable, wherein the eighth shaft is connected toboth the sun gear of the first planetary gear set and the sun gear ofthe second planetary gear set, and the eighth shaft can be detachablyconnected, via a third clutch, to the drive shaft, the drive shaft isdetachably connectable, via a first clutch, to the fourth shaft, thefourth shaft is connected to the carrier of the first planetary gear setand the fourth shaft is couplable, via a second brake, to the housing,the drive shaft is detachably connectable, via a second clutch, to theseventh shaft, the seventh shaft is connected to both the carrier of thefourth planetary gear set and the ring gear of the third planetary gearset, the sixth shaft is connected to each of the ring gear of the firstplanetary gear set, the carrier of the second planetary gear set and thering gear of the fourth planetary gear set, the third shaft is connectedto both the sun gear of the third planetary gear set and the sun gear ofthe fourth planetary gear set, and the third shaft can be coupled, via afirst brake, to the housing, the fifth shaft is connected to the ringgear of the second planetary gear set and is couplable, via a thirdbrake, to the housing, and the drive shaft is directly connected to thecarrier of the third planetary gear set.
 19. The multi-stagetransmission according to claim 18, wherein a first forward gear isattained by engaging the first and the third brakes and the thirdclutch, a second forward gear is attained by engaging the first and thethird brakes and the first clutch, a third forward gear is attained byengaging the first brake and the first and the third clutches, a fourthforward gear is attained by engaging the first brake and the second andthe third clutches, a fifth forward gear is attained by engaging thefirst, the second and the third clutches, a sixth forward gear isattained by engaging the third brake and the first and the secondclutches, a seventh forward gear is attained by engaging the third brakeand the second and the third clutches, an eighth forward gear isattained by engaging the second and the third brakes and the secondclutch, a ninth forward gear is attained by engaging the second brake(04) and the first and the third clutches, and the reverse gear isattained by engaging the first and the second brakes and the thirdclutch.
 20. The multi-stage transmission according to claim 18, whereina first forward gear is attained by engaging the first and the thirdbrakes and the third clutch, a second forward gear is attained byengaging the first and the third brakes and the first clutch, a thirdforward gear is attained by engaging the first brake and the first andthe third clutches, a fourth forward gear is attained by engaging thefirst and the second brakes and the second clutch, a fifth forward gearis attained by engaging the first, the second and the third clutches, asixth forward gear is attained by engaging the third brake and the firstand the second clutches, a seventh forward gear is attained by engagingthe third brake and the second and the third clutches, an eighth forwardgear is attained by engaging the second and the third brakes and thesecond clutch, a ninth forward gear is attained by engaging the secondbrake (04) and the first and the third clutches, and the reverse gear isattained by engaging the first and the second brakes and the thirdclutch.
 21. The multi-stage transmission according to claim 18, whereina first forward gear is attained by engaging the first and the thirdbrakes and the third clutch, a second forward gear is attained byengaging the first and the third brakes and the first clutch, a thirdforward gear is attained by engaging the first brake and the first andthe third clutches, a fourth forward gear is attained by engaging thefirst brake and the first and the second clutches, a fifth forward gearis attained by engaging the first, the second and the third clutches, asixth forward gear is attained by engaging the third brake and the firstand the second clutches, a seventh forward gear is attained by engagingthe third brake and the second and the third clutches, an eighth forwardgear is attained by engaging the second and the third brakes and thesecond clutch, a ninth forward gear is attained by engaging the secondbrake (04) and the first and the third clutches, and the reverse gear isattained by engaging the first and the second brakes and the thirdclutch.
 22. The multi-stage transmission according to claim 18, whereina first forward gear is attained by engaging the first and the thirdbrakes and the third clutch, a second forward gear is attained byengaging the first and the third brakes and the first clutch, a thirdforward gear is attained by engaging the first brake and the first andthe third clutches, a fourth forward gear is attained by engaging thefirst and the third brakes and the second clutch, a fifth forward gearis attained by engaging the first, the second and the third clutches, asixth forward gear is attained by engaging the third brake and the firstand the second clutches, a seventh forward gear is attained by engagingthe third brake and the second and the third clutches, an eighth forwardgear is attained by engaging the second and the third brakes and thesecond clutch, a ninth forward gear is attained by engaging the secondbrake (04) and the first and the third clutches, and the reverse gear isattained by engaging the first and the second brakes and the thirdclutch.
 23. The multi-stage transmission according to claim 18, whereinthe multi-stage transmission is an automatic transmission for a motorvehicle.